Ultrasound therapy is a powerful technique that uses acoustic energy to provide medical treatment. Ultrasound therapy typically uses an ultrasound transducer or probe to radiate the acoustic energy to a treatment region. Various design parameters of the transducer impact the attainable level of control. For example, the amplitude, temporal control and spatial harnessing of the acoustic energy can be varied depending upon the treatment desired. In addition, the acoustic power output capability, the allowable frequency range of operation, and the size and shape of the power output of the transducer can be varied to provide a desired acoustic radiation pattern.
An ultrasound transducer typically includes a transduction element having a piezoelectrically active layer, such as lead zirconante titanate (PZT). The piezoelectrically active layer receives electrical drive signals that cause the piezoelectrically active layer to expand and contract, and thus convert the electrical drive signals to mechanical waves. These mechanical waves are ultimately acoustically coupled to a tissue region. The piezoelectric layer is typically hard compared to the tissue, which entails the use of acoustic matching layers and backing materials to dampen any high-Q resonances and extend the useful bandwidth of operation for the transducer.
To achieve ultrasound ablation or collagen reformation effects in tissue, a relatively high power output is required as compared to the ultrasound acoustic power levels needed for diagnostic applications. Many backing materials, such as rubber, that are configured within ultrasound transducers tend to absorb a large amount of the power, thus resulting in heating of the backing material as well as an active transduction layer. This heating of the backing material can cause the transducer to overheat and destruct, and cause the transducer to have a low efficiency and a reduced power output. One alternative to backing materials has been to configure the transducers as unloaded or “air-backed.” However, such air-backed transducers have reduced bandwidths.
Moreover, conventional transducers are configured for providing radiation in only a single-direction. For example, with reference to a block diagram of an ultrasound system 100 illustrated in FIG. 1, a conventional transducer 102 is configured to provide therapy only to a single region of interest 104, i.e., configured to provide acoustic energy in only one direction. Conventional transducers are limited to single direction radiation whether having backing materials or being air-backed.
For example, with reference to FIG. 2, a conventional transducer 200 comprises a transduction element 202 configured as an air-backed transducer, i.e., having an air-backing 208, and having electrical leads 206. Air-backing 208 is configured with transduction element 202 on one side, thus allowing transducer 200 to only transmit energy in a single radiation pattern 204 on a side opposite that of air-backing 208. Conventional backing materials also limit such transducers 200 to single-direction radiation, with the backing material configured on a first side, and transducer 200 generating radiation from a second side towards a single treatment region. To address other treatment regions, transducer 200 requires significant rotational or translational movements to provide such treatment, thus requiring a significant amount of time and power.